JP2001285249A - Method for generating transmission signal, and generator for the transmission signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate deterioration in a modulation characteristics caused by a difference from an arithmetic time between an in-phase signal and a quadrature signal from a digital orthogonal modulator. SOLUTION: The transmission signal generator is configured with a signal point setting means (12) that sets a compensation signal point to correct an error in a signal point arrangement position depending on the signal point arrangement position error caused by an arithmetic timing error of the digital orthogonal modulator, and a mapping means (11) that assigns a digital information signal to be sent on the basis of the signal point setting means. The signal generator performs a digital modulation (13) and a digital orthogonal modulation (15) on the basis of the signal point information assigned by the data mapping means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature digital modulation system for modulating two orthogonal digital information signals with one carrier, and more particularly, to interference, crosstalk, etc., between two modulated digital information signals. The present invention relates to a method for compensating for a phase error in a quadrature modulated signal that causes distortion, a method for generating a transmission signal having a means for compensating the phase error, and a transmission signal generation device.

[0002]

2. Description of the Related Art In recent years, with the advancement of digital signal processing technology, a high-efficiency digital modulation method for transmitting digital information to a high-efficiency compression-coded digital video and audio has been realized. Is desired. The high-efficiency digital modulation method is a modulation and demodulation method capable of transmitting a digital signal having a large amount of information in a predetermined frequency band with a small error rate.

As one of them, one carrier signal is divided into two.
There is a two-phase modulation system that modulates with a type of information signal, and the modulation system is used for transmitting two color difference signals in the analog television system of the current NTSC system.
Two types of color signals are transmitted by one subcarrier.

A method of regarding these two kinds of color signals as two kinds of digital signals and modulating and transmitting one subcarrier signal in the amplitude modulation direction and the phase modulation direction is called QAM (quadrature amplitude modulation). Are known.

Here, a system for performing QAM modulation on each of a large number of subcarriers with a large number of two types of digital signals and transmitting the signals is an orthogonal frequency division multiplexing modulation (OFD) system.
M), and the frequency of the digitally modulated signal performed here can be lowered by the number of subcarriers. Therefore, even if a guard interval period is provided, a decrease in transmission efficiency can be kept small, and multipath A wireless transmission path that is not affected by distortion can be secured.

The OFDM system can reduce the frequency of the digital modulation signal, thereby reducing the interference with adjacent channels, such as making the transmission frequency spectrum rectangular, thereby realizing a highly efficient digital modulation system with good bandwidth utilization. can do.

It is important to realize a modulation scheme having such characteristics on a small circuit scale in terms of mobile communication applications using these modulation schemes. If it can be realized by a quadrature modulation circuit, the digitized modulation circuit can be made into an LSI, and the size and power consumption of the modulation circuit can be reduced.

The present applicant has filed an application for digital orthogonal modulation technology in August 1999 as “Orthogonal Frequency Division Multiplexing Modulation Method and Orthogonal Frequency Division Multiplexing Modulator” (Japanese Patent Application H1).
1-238098) has a feature that the circuit configuration can be simplified since the multiplication of the sine wave and the cosine wave performed inside the digital modulator can be performed using the values of 1, 0, and -1. is there.

[0009]

By the way, a digital quadrature modulator using a small-sized and power-saving LSI as described above is suitable for a small-sized and power-saving LSI as the frequency of a signal to be handled is small. Attempts have been made to realize a circuit whose operating frequency is as low as possible. However, in a quadrature digital modulation circuit using such a low frequency, an error is caused by setting the operating frequency to be low, thereby deteriorating the characteristics of the modulation circuit.

The cause of the deterioration of the modulation characteristics will be described. In a multi-carrier transmission system represented by an OFDM transmission system, a modulated signal is generated as a time-series signal by an inverse Fourier transform of a signal in phase with a subcarrier and a signal orthogonal to the subcarrier. The signal represented by the series is supplied to a digital quadrature modulation circuit.

The in-phase signal and the quadrature signal generated here are:
These signals are obtained as sampling data at the same time, and these signals are multiplied by a signal having a phase difference of 90 degrees with a signal corresponding to the modulation frequency in a digital quadrature modulator. A timing phase difference corresponding to one sample of the present signal occurs.

This timing phase difference is described in
The digital processing quadrature modulator is also described, and a digital filter is used to realize a highly efficient digital modulator, and the problem of the timing phase difference is to be solved.

However, the digital filter for compensating for the timing phase difference generated as described above requires a high-precision operation, which makes the device complicated and expensive. Also, for example, when a digital filter is inserted only on the quadrature signal side, although the timing phase difference can be absorbed, it is difficult to flatten the amplitude frequency characteristics of the filter, and the digital modulation characteristics are deteriorated due to the disturbance of the amplitude characteristics. It has not been used effectively.

[0014]

The present invention comprises the following means 1) to 5) to solve the above-mentioned problems. That is,

1) A two-dimensional plane having a real part signal and an imaginary part signal as axes is divided into a plurality of regions, and a central position for designating each of the divided regions is defined as a signal point. As well as, according to the content of the digital information signal to be transmitted, sequentially allocated to a specific signal point of the plurality of signal points, a real part signal and an imaginary part signal at each of the sequentially allocated signal points. In the transmission signal generation method for generating a transmission signal obtained by converting signal point information into a high-frequency signal by performing digital modulation and digital quadrature modulation, digital modulation is performed on the signal point information assigned to the position of the signal point. And a modulation signal point obtained by performing digital quadrature modulation is determined as a compensation signal point at a position that is a point target with respect to the position of the signal point.
(12), a second step (11) of allocating the digital information signal to be transmitted to the compensation signal point determined in the first step, and the compensation signal allocated in the second step A third step (13, 15) of digitally and quadrature-modulating signal point information at points to generate a high-frequency signal.

2) The position of the compensation signal point in the first step may be a phase difference and an amplitude difference between an in-phase signal and a quadrature signal generated by the digital modulation and the digital quadrature modulation, or a position of the digital quadrature modulator. The transmission signal generation method according to claim 1, wherein the signal point is a position of a signal point where an error generated by the orthogonality difference is compensated.

3) The position of the compensation signal point in the first step is a position of a signal point in which an error caused by a timing difference between an in-phase signal and a quadrature signal processed by the digital quadrature modulation is compensated. The transmission signal generation method according to claim 1, wherein:

4) A two-dimensional plane centered on the real part signal and the imaginary part signal is divided into a plurality of regions, and for each of the divided regions, a central position for designating the region is defined as a signal point. And sequentially assigns a first-system digital information signal to be transmitted to a specific signal point among the plurality of signal points according to the content thereof, and a real part signal and an imaginary number at each of the sequentially assigned signal points. The first signal point information, which is a partial signal, is converted to the first signal point information by the first carrier frequency.
A digital information signal of the second system to be generated and transmitted as a modulated signal according to the content is sequentially allocated to a specific signal point among the plurality of signal points, and a real number at each of the sequentially allocated signal points is allocated. Digital modulation means for generating second signal point information composed of a partial signal and an imaginary part signal as a second modulation signal using a second carrier frequency having the same frequency as the first carrier frequency but different in polarity; A digital quadrature modulation of the first and second modulation signals generated by the digital modulation means to generate a transmission signal converted into a high-frequency signal; The first and second signals obtained by performing digital modulation and digital quadrature modulation on the signal point information assigned to the positions of the signal points related to the two systems of digital information signals. A first step (12) of defining two modulation signal points as first and second compensation signal points at positions symmetrical with respect to the positions of the respective signal points; A second step (11) of allocating two systems of digital information signals to the first and second compensation signal points determined in the first step, and the first and the second allocated in the second step. A third step (1) of generating the high-frequency signal by digitally and quadrature-modulating each signal point information at the second compensation signal point;
(3, 15).

5) A two-dimensional plane centered on the real part signal and the imaginary part signal is divided into a plurality of regions, and a central position for designating each of the divided regions is a signal point. As well as, according to the content of the digital information signal to be transmitted, sequentially allocated to a specific signal point of the plurality of signal points, a real part signal and an imaginary part signal at each of the sequentially allocated signal points. In a transmission signal generating apparatus for generating a transmission signal obtained by converting signal point information comprising a digital signal and a digital quadrature modulation into a high-frequency signal, the signal point information assigned to the signal point position is digitally modulated. And a compensation signal point setting means (1) that determines a modulation signal point obtained by performing digital quadrature modulation as a compensation signal point at a position that is a point target with respect to the signal point position. 2), mapping means (11) for allocating the digital information signal to be transmitted to the compensation signal points set by the compensation signal point setting means, and signal point information at the compensation signal points allocated by the mapping means. -Frequency signal generation means (13, 15) for generating a high-frequency signal by digitally and quadrature-modulating the signal
And a transmission signal generation device, comprising:

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a transmission signal generation method and a transmission signal generation apparatus according to the present invention will be described below with reference to preferred embodiments. FIG. 1 is a schematic configuration of an orthogonal frequency division multiplex modulation apparatus according to the embodiment, and its configuration and operation will be outlined.

This orthogonal frequency division multiplexing and modulation apparatus includes a data mapping circuit 11, a mapping table 12, an IFF
It comprises a T operation circuit 13, a digital quadrature modulation circuit 15, an intermediate frequency oscillator 16, and a DA converter 17.

The operation of the orthogonal frequency division multiplex modulation apparatus thus constructed will be described. Digital data to be modulated is supplied to a data mapping circuit 11, where the data constitutes an orthogonal frequency division multiplex signal. Of which carrier is allocated and transmitted, the position of the signal point of the QAM-modulated carrier is determined according to the value of the digital data to be modulated for each carrier, and these signals are determined. Signals i and q corresponding to the position in the amplitude direction corresponding to the position of the point and the position in the angular direction
Is generated and supplied to the IFFT operation circuit 13.

Here, each carrier constituting the orthogonal frequency division multiplexing is orthogonally frequency-modulated at a given signal point in accordance with the supplied signals i and q, and each carrier is converted into a real part signal R and an imaginary part signal. Baseband signal outputs synthesized as I are obtained, and these baseband signal outputs are supplied to the digital quadrature modulator 15. Here, the real part signal R and the imaginary part signal I, which are the baseband signal outputs, are converted into a signal in a frequency band centered on the frequency oscillated by the intermediate frequency oscillator 16 and converted into a signal in a new frequency band. The digital quadrature modulation signal is a DA converter 1
7, the signal is converted into an analog signal and output.

Here, a mapping table 12 connected to the data mapping circuit 11 is a table in which data for correcting in advance a characteristic error caused by a digital quadrature modulator described later is stored. A signal mapped by the circuit 11 is corrected according to a predetermined rule to correct a characteristic error of the digital quadrature modulator, thereby realizing a digital modulation device having good characteristics.

The transmission signal generated in this manner is supplied to a receiving device, and the supplied high-frequency signal is demodulated to obtain the transmitted signal point information. The transmission signal signal is transmitted from the obtained signal point information. It is configured to decode and obtain the obtained digital information signal.

Here, the change in characteristics caused by the digital quadrature modulation circuit will be described in comparison with a conventional analog quadrature modulator. First, in the case of a conventional analog quadrature modulator, the analog quadrature modulator includes an IFF in the form of a digital signal.
The signal output from the T calculator 13 is supplied with a signal converted to an analog signal by the DA converter 17, and the supplied signal is converted into a signal having a frequency band centered on the intermediate frequency oscillation frequency supplied from the intermediate frequency oscillator. It was converting to a signal.

FIG. 2 shows a circuit of the analog quadrature modulator.
In the figure, for example, a baseband signal supplied from an IFFT operator 13 is converted into an analog signal by a DA converter 17, and the converted real part signal R has an angular frequency ωt supplied from an intermediate frequency oscillator 16. The cosine signal is multiplied by a 90-degree phase shifter with a sine wave signal having an angular frequency of ωt, and the imaginary part signal (I) converted into an analog signal has an angular frequency of ωt supplied from the intermediate frequency oscillator 16. Is multiplied by a cosine wave signal, and the operation outputs obtained from the two multipliers are added by an adder and output as a quadrature modulation output signal.

Here, the sine wave output signal corresponding to the cosine wave output signal supplied from the intermediate frequency oscillator is generated by using a 90-degree phase shifter. Since the characteristics tend to fluctuate due to fluctuations in the circuit constants of the analog multipliers, it is also difficult to obtain stable quadrature modulation output signals over a long period of time due to the high frequency characteristics of analog multipliers. It has been desired to realize a digitized quadrature modulation circuit that is hardly affected.

FIG. 3 shows the configuration of a quadrature modulator composed of digital circuits. In the figure, I is the signal of the real part supplied from the IFFT 13, Q is the signal of the imaginary part, and the respective I and Q signals are shown as an amplifier with an amplification of 1 and with an amplification of -1. Supplied to the inverting amplifiers, and I, -Q,-
Four signals of I and Q are obtained.

These four signals are supplied to a data selector, and the data selector outputs these four signals while sequentially switching them according to the cycle of the oscillation frequency supplied from the intermediate frequency oscillator. That is, first the signal I, then-
The operation of outputting Q, then -I, and finally Q is repeated.

FIG. 4 is a timing chart of the digital quadrature modulator operating as described above. In the figure, a time interval described as a sample period is a period corresponding to the sampling frequency of the orthogonal frequency division multiplexed signal,
The period corresponds to 1 / n of a window section for operating the n-point IFFT circuit.

In this figure, the signal is represented by a subscript suffix of n-1, n, n + 1, where I is the real part output signal from the IFFT operation unit 13 and the operation period is a sampling period. Similarly, the imaginary part output signal Q from the IFFT operator 13 has the same n−1, n, n +
It is shown with a subscript of 1.

The signal indicates the signal I obtained by amplifying the signal I by the amplifier and the signal obtained when the inverted signal -I is switched a plurality of times within the sampling period by the data selector. _{I n, 0, -I n,} 0 is,
I _n ,, 0, -I _n, are repeated as of ...,
This signal every 90 degrees of the values of the cosine function I _n, 1, 0,
-1, 0,... Are multiplied.

Similarly, the signals are 0, -Qn, 0, Qn,
0, −Qn, 0,... The signal obtained by adding the signal thus obtained to the signal is a signal,
The signal _{I n, -Q n, -I n} , Q n, I n, -Q n, -
I _n, has a ...., which is the output signal of the quadrature modulator.

Here, when the signal is repeatedly switched many times in one sample period as shown in this example, the modulation characteristic difference given to the I and Q signals by the switching order of the signal is small, If the sampling period is short and the number of signal switching repetitions cannot be increased many times during the sampling period, a characteristic difference occurs in the modulated signal obtained from the digital quadrature modulation circuit, and the characteristic of the difference is corrected. Signal processing is required.

The present embodiment realizes a digital quadrature modulator having good characteristics by correcting such a difference in characteristics. The correction of the characteristics is achieved by the signal appearing at the start point of the sample period in FIG. , The signal relating to the time error caused by the signal of the real part always appearing earlier than the signal of the imaginary part, such that the signal of the real part I _n first and then the signal of the imaginary part Q _n The difference in characteristics due to the phase shift is compensated for.

The characteristic shift in the output of the digital modulation signal caused by such a time difference is defined by the data mapping circuit 11, and the relationship between the i signal and the q signal supplied to the IFFT is corrected. And performs compensation so that the digital quadrature-modulated modulation signal becomes a normal modulation signal.

That is, the difference in characteristics caused by the time difference between the I signal and the Q signal generated in the digital quadrature modulator at this time is the timing error of the sine wave of the digital quadrature modulation section. It is also an error for the orthogonality of the I and Q signal vectors. This orthogonality error occurs between the sidebands of the modulated signal that are present at the same positive and negative frequencies with respect to the frequency of the intermediate frequency oscillator.
The sideband signal of the negative frequency leaks as a crosstalk component to the sideband of the positive frequency, and the frequency spectrum component of the modulated wave signal changes, so that this leaked signal level is canceled. I do.

This crosstalk component also exists from a sideband having a negative frequency to a sideband having a positive frequency. Accordingly, the data mapping characteristics for correcting these crosstalks in advance have the same frequency difference with respect to the center carrier, and the polarity of the frequency difference is different for the corresponding subcarriers having different polarities. It is necessary to perform characteristic compensation.

As a method of arranging signal points in data mapping for generating a modulation signal having a positive / negative pair of frequencies, for example, when expressing a signal point arrangement by coordinates on a complex plane, a real part signal and an imaginary part For signals that should be assigned as (1,1) with equal signals, (1
(+ X, 1 + y) so that the real part signal is given x and the imaginary part signal is given y.

In this manner, the signals of the real part and the imaginary part for the corresponding subcarriers having positive and negative frequencies are expressed as follows. (Real number of positive frequency, imaginary number of positive frequency, real number of negative frequency, imaginary number of negative frequency) = (d1 + x, d2 + y, d
3 + x ', d4 + y')

Here, d1, d2, d3 and d4 are values for giving a normal signal point arrangement, for example, QPSK.
In the case of a digital modulation method using (quadrature phase shift keying), d1, d2, d3, and d4 take one of +1 and -1. Then, regarding the values of the compensation signals represented by x, x ′, y, y ′,
It will be described in detail.

As shown in FIG. 4, the output signal of the quadrature modulator is determined by the position at which the I signal and the Q signal appear with respect to the start position of the sample period, by the hardware for controlling the operation of the digital quadrature modulator. It is uniquely determined by the configuration of the software or by the configuration of the control program software for controlling the operation of the digital modulator, and generally the order is fixed.

For example, there is a method of making the order of appearance random, but in such a case, the above-described difference in characteristics is obtained as noise with respect to the modulated signal. In addition, there is a method of reversing the order of appearance of the I signal and the Q signal. In that case, however, an error signal having the opposite polarity is generated, and in any case, the modulation signal needs to be compensated.

As described above, since the I signal and the Q signal, which are data at the same time, are processed by the digital quadrature modulator as data at different times, the orthogonality of the R signal and the I signal is changed by the modulation frequency. It will differ by one sample time, and it is necessary to compensate for the time difference.

In this case, the time difference is compensated for in a small sample period, and the digital modulation circuit uses I,
When the number of switching repetitions of the Q signal cannot be increased, the ratio of the appearance time difference between the I and Q signals to the sample period increases, and the compensation signal level of the modulation error also increases.

FIG. 5 shows a specific operation example. In the figure, the sampling period is 19.5 nsec, that is, the sampling frequency is 51.2 MHz, and the IFFT operation circuit outputs a real part signal as an operation result and a signal as an imaginary part signal every 19.5 nsec.

For each sample period of this IFFT operation circuit,
Obtained, I_n, I_{n + 1}, I_{n + 2}, I_{n +3},····,as well as
Q_n, Q_{n + 1}, Q_{n + 2}, Q_{n + 3}, ...
Is considered as pulling data, that is, its sampling
Data includes signal components from DC up to 16 MHz
Assume that the signal is a baseband signal, and
Centered around 25.6 MHz which is the oscillation frequency of the oscillator
Convert to frequency band signal.

At this time, the band of the frequency-converted signal is 25.6 ± 16 MHz, the sampling frequency of the converted data sequence is 102.4 MHz, and the orthogonality error generated at this time is about 9 .8 ns (1/10
2.4 MHz).

Therefore, this orthogonality error is equal to the center frequency 2
38.4 MHz 12.8 MHz higher than 5.6 MHz
Has a phase delay of π / 4 radian with respect to the subcarrier having the frequency of 12.8.
The phase advance of π / 4 radian is obtained for a subcarrier having a frequency lower than MHz, and a digital quadrature modulation circuit needs to be provided with a compensation function for correcting the phase difference generated as described above.

Here, the necessary compensation amount will be described. First, the compensation amount is expressed by a two-dimensional plane including a real axis and an imaginary axis. FIG. 6 has a phase angle of α, and the angular velocity +
The state of a subcarrier rotating at ω _n and having an amplitude of A is shown on a two-dimensional plane with imaginary and real axes. That is, the subcarrier signal is represented as in equation (1). _{A × cos (+ ω n t} + α) + j × A × sin (+ ω n t + α) (1)

Here, the subcarrier is QPSK (qu
adrature phase shift keying)
A is 1.41 (square root of 2) and α is π / 4, 3π / 4, 5π
Takes one of the values of / 4 and 7π / 4.

Similarly, a subcarrier signal rotating at an angular velocity of -ω _n , having an amplitude of B, and having a phase angle of β is expressed by equation (2). _{B × cos (-ω n t +} β) + j × B × sin (-ω n t + β) (2)

Here, subcarriers in the case where there is an error in the amplitude and phase of the imaginary part signal with respect to the real part signal will be described. That is, the amplitude change of the imaginary part signal is λ times,
This is a case where the phase angle shift is γ radian. At this time, the subcarrier whose angular velocity is + ωn is _expressed by equation (3), and the subcarrier whose angular velocity is -ωn is _expressed by equation (4).

[0055] _{A × cos (+ ω n t} + α) + j × λ × A × sin (+ ω n t + α-γ) (3) B × cos (-ω n t + β) + j × λ × B × sin ( −ω _n t + β + γ) (4) where γ is the above-mentioned sampling period (about 9.8 ns)
Is an arithmetic error that occurs based on the above equation, and it is necessary to compensate for this error.

Next, these subcarrier signals are represented by exponential functions, which will be further described. First, when Expression (1) is represented by an exponential function, Expression (5) is obtained. ^{(A + jb) × e j} ω nt (5) where a = A × cos α, which is b = A × sin α.

Next, when the trigonometric function of Expression (3) is expanded and expressed by an exponential function, Expression (6) shown in FIG. 7 is obtained. Similarly, the expression (4) is expanded to obtain the expression (7) shown in FIG.
These equations are each composed of four terms, ie, terms 61, 62, 63, 64 and terms 71, 72, 73, 74.

In equation (6), terms 61 and 63 are vectors rotating at an angular velocity ωt, and the vectors are shown in FIG. In the drawing, the vector 61 has an amplitude (vector length) of A / 2, and the angle from the real axis is indicated as α. Similarly, the vector 63 has an amplitude of λ × A / 2.
The angle from the real axis is α-γ.

Bold lines 62 and 64 shown in FIG.
, And the angle from the real axis is as follows: the vector 62 is −α, and the vector 64 is − (α−γ).
, And the vector of the second quadrant.

Further, the vector 72 shown in FIG.
1 represents a real part signal, and FIG.
The imaginary part signal is represented by a vector 73 of 1 and a vector 74 of FIG. Similarly, in equation (7), terms 71 and 7
Reference numeral 3 denotes a vector rotating at an angular velocity -ωt, and the vector is shown in FIG.

The terms 72 and 74 in the equation (7) are vectors rotating at the angular velocity ωt, and the vectors are shown in FIG. Then, the vector 61 of FIG.
The vector 62 represents the real part signal of Equation 1 described above, and the vector 63 of FIG. 8 and the vector 64 of FIG. 9 represent the imaginary part signal.

In this manner, the error of the modulated signal caused by the operation time not being the same between the real part signal and the imaginary part signal of the digital quadrature modulator is calculated by the term 63
64, λ is a number other than 1 and γ is a number other than 0. Compensating the error of the modulation signal based on the operation timing of the digital quadrature modulator is to provide a means for canceling such an error generated in the digital quadrature modulator, and the method will be described below.

Specifically, for the term 63, the amplitude is 1 /
If a signal whose phase is advanced by γ at λ times is given, the amplitude is increased by λ by the digital quadrature modulator and the phase is delayed by γ,
A signal in which λ and γ are eliminated from the term 63 is obtained. Providing such a signal for compensating for λ and γ,
Expression (8) with respect to Expression (6) shown in FIG.
Equation (9) is applied to (7).

This is a signal having a characteristic in which the amplitude λ and the phase angle γ are canceled out with respect to the characteristics according to the above-described equations (3) and (4), and is digitally orthogonal according to the above-described equations (1) and (2). This means that a modulated signal with modulation is obtained, and the error signal component caused by the signal processing of the real part and the imaginary part at different times in the digital quadrature modulator is equivalently canceled. Because.

FIG. 12 shows mapping points for obtaining a signal output of angular frequency ωt compensated by the digital quadrature modulator. In the drawing, the vector 101 to be set is obtained by combining the vectors of 81, 83, 92, and 94. The vectors 81 and 83 are terms including e ^j ω ^t in the equation (8), and the vector 92 and 94 is such that in the section including e ^j omega ^t in equation (9), the vector 101 is obtained by combining the vector rotating at an angular velocity + .omega.t.

That is, the vector 101 is the vector 8
1 and a vector 92, and a vector 83
A vector 101 is obtained by synthesizing the vector 101 and the vector obtained by synthesizing the vector 94. The obtained vector 101 is a correction position of a signal point to be given to a subcarrier rotating at an angular velocity ωt.

FIG. 13 shows mapping points for obtaining a signal output of angular frequency -ωt compensated by the digital quadrature modulator. In the figure, signal points 102 to be set (8), which was determined by combining the vectors 82,84,91,93 corresponding to the term including e ^-j omega ^t in (9), angular This is to provide a corrected signal point for performing modulation on the subcarrier rotating at the frequency -ωt.

[0068] In this way, the sub-carrier B subcarrier _{A × cos (+ ω n t} + α) + j × A × sin (+ ω n t + α) and the angular frequency angular frequency is omega _n is - [omega] _{n × cos (-ω n t + β} ) + j × B × sin in order to obtain the (-ω _n t + β), the sub-carrier angular frequency is _{ω n a × cos (+ ω} n t + α) + j × ( 1 / λ) × A × sin (+ ω _n t
+ Α + γ) Further, a subcarrier having an angular frequency of −ω _n is represented by B × cos (−ω _n t + β) + j × (1 / λ) × B × sin (−ω _n t
+ Β-γ), the amplitude and phase of the Q signal may be corrected.

Next, in the above equations (8) and (9), subcarrier signal components relating to each frequency + ω _n are selected, and a composite signal of the selected signal components is obtained as follows. (A / 2) × e ^j α + (B / 2) × e ^-j β + (1 / λ) × (A / 2) × e ^{j (} α ⁺ γ ⁾ − (1 / λ) × (B / 2) × e ^{-j (} β ^- γ ⁾ = (A / 2) × (cosα + jsinα) + (B / 2) × (cosβ-jsinβ) + (1 / λ) × (A / 2) × (cos (α + γ) + jsin (α + γ)) − (1 / λ) × (B / 2) × (cos (β−γ) −jsin (β−γ)) = (A / 2) × cosα + (B / 2) × cosβ + (1 / λ) × (A / 2) × cos (α + γ) − (1 / λ) × (B / 2) × cos (β−γ) (10) + j × ((A / 2) × sinα− (B / 2) × sinβ + (1 / λ) × (A / 2) × sin (α + γ) + (1 / λ) × (B / 2) × sin (β−γ)) (11)

Similarly, in equations (8) and (9),
Subcarrier signal components related to each frequency −ω _n are selected, and a composite signal of the selected signal components is obtained as follows. (B / 2) × e ^j β + (A / 2) × e ^-j α + (1 / λ) × (B / 2) × e ^{j (} β ^- γ ⁾ − (1 / λ) × (A / 2) × e ^{-j (} α ⁺ γ ⁾ = (B / 2) × (cosβ + jsinβ) + (A / 2) × (cosα-jsinα) + (1 / λ) × (B / 2) × (cos (β-γ ) + Jsin (β−γ)) − (1 / λ) × (A / 2) × (cos (α + γ) −jsin (α + γ)) = (B / 2) × cosβ + (A / 2) × cosα + (1 / λ) × (B / 2) × cos (β−γ) − (1 / λ) × (A / 2) × cos (α + γ) (12) + j × ((B / 2) × sinβ− (A / 2) × sin α + (1 / λ) × (B / 2) × sin (β−γ) + (1 / λ) × (A / 2) × sin (α + γ)) (13) Becomes

Here, equation (10) is a numerical value assigned to the real part of the + ω _n subcarrier component, and equation (11) is
+ Ω _n is a numerical value assigned to the imaginary part of the subcarrier component, Equation (12) is a numerical value assigned to the real part of the −ω _n subcarrier component, and Equation (13) is a imaginary part of the −ω _n subcarrier component. Is a numerical value assigned to.

In this way, the angular frequencies are + ω _n and −ω _n
The signal levels of the real part component and the imaginary part component of the subcarrier are obtained. However, since the error component of the digital quadrature modulator shown in FIG. 3 is related to the operation time of the imaginary part signal, no error occurs in the amplitude. Therefore, λ = 1 and γ has a predetermined value other than 0.

When the digital quadrature modulator shown in this example is QPSK, A and B take the same value.
= B, Expressions (10) to (13) are respectively expressed by Expression (1).
4) to (17).

(A / 2) × (cosα + cosβ + cos (α + γ) −cos (β−γ)) (14) + j × (A / 2) × (sinα−sinβ + sin (α + γ) + sin (β− γ)) ・ ・ ・ ・ (15) (A / 2) × (cosβ + cosα + cos (β-γ) -cos (α + γ)) ・ ・ ・ ・ ・ ・ (16) + j × (A / 2) × (sinβ-sinα + sin (β−γ) + sin (α + γ)) (17)

Further, the modulation angle given in the case of the QPSK modulation method is any one of π / 4, 3π / 4, 5π / 4 and 7π / 4, and the angles α and β are 4 × 4 Will be selected in combination.

The table shown in FIG. 14 shows that when the frequencies of such positive and negative subcarriers are modulated by the QPSK system, each carrier specifies four signal points, and 16 types of It can be divided, but 16
This is shown for each type.

That is, in the same table, the four mathematical expressions in each frame are, from the top, the expressions (14), (15), (1)
6) and (17), and γ takes different values depending on the frequency of each subcarrier.

In this embodiment, for ease of explanation, an example in which the present invention is applied to QPSK modulation has been described. However, the modulation method is not limited to this, and it can be applied to BPSK modulation, multi-level QAM modulation, and the like. Needless to say.

Further, the compensation of the characteristic difference due to the difference in the operation timing is not limited to the technique targeting the multi-carrier, and a frequency which is positive with respect to the center carrier and a frequency which is negative with respect to the center carrier are set. Then, the present invention can be applied to a modulation scheme in which signal point arrangement is determined for each subcarrier frequency to transmit information.

Further, in the present embodiment, as an example when there is no amplitude error, the table is shown in FIG. 14 described above, limiting to λ = 1. The signal point to be set is obtained, and the amplitude difference can be compensated simultaneously with the phase compensation.

As described above, according to the apparatus of the present embodiment, the baseband signals of the real part and the imaginary part obtained by digital orthogonal modulation using, for example, IFFT are converted to digital orthogonal frequency division signals of the intermediate frequency band as digital signals. When converting to a multiplex modulated signal, the digital quadrature modulator
Even when a digital quadrature modulation signal is generated by alternately calculating a real part signal and an imaginary part signal from the FFT calculator, an error signal generated due to a difference between the calculation timings of the real part signal and the imaginary part signal is calculated as follows. In order to perform an IFFT operation by providing a signal point arrangement for canceling the operation error when a signal of a real part and an imaginary part is generated in advance by IFFT,
It is possible to obtain a stable and accurate digital orthogonal division multiplex signal by digital orthogonal modulation signal generation processing that does not include an error signal.

Further, the phase difference between the in-phase signal and the quadrature signal generated by the digital modulation and the digital quadrature modulation,
A position error caused by an amplitude difference or an orthogonality difference due to the digital modulation and the digital orthogonal modulation can be compensated.

Further, the position error caused by the interference between two subcarriers set at the same frequency interval in the positive direction and the negative direction with respect to the center carrier used when transmitting the modulated signal is described above. According to the table shown in FIG. 14, by performing digital modulation using a mapping table value set according to the modulation signal given to the opposing subcarrier, digital orthogonality compensated for a position error caused by interference between both carriers. A modulated signal can be generated.

Although the digital quadrature modulator in the above embodiment has been described as having a configuration in which digital modulation is performed using data of an I signal followed by a Q signal, the signal processing sequence of the digital quadrature modulator is A similar effect can be obtained even if the arithmetic processing is performed first, and then the arithmetic processing using the I signal data is performed.

[0085]

According to the first aspect of the present invention, for example, I
When converting the real part and imaginary part baseband signals obtained by digital quadrature modulation by FFT or the like to digital quadrature frequency division multiplexing modulated signals in the intermediate frequency band as digital signals, the digital quadrature modulator IFFT
Even when a signal of a real part and a signal of an imaginary part from an arithmetic unit are alternately operated to generate a digital quadrature modulation signal,
An error signal generated by the difference between the operation timings of the real part signal and the imaginary part signal is subjected to IFFT calculation by providing a signal point arrangement for canceling the operation error when the real part and imaginary part signals are generated in advance by IFFT. By doing
There is an effect that it is possible to provide a method for obtaining a stable and accurate digital quadrature modulation signal by digital quadrature modulation signal generation processing that does not include an error signal.

According to the second aspect of the present invention, in particular, a position error caused by a phase difference and an amplitude difference between an in-phase signal and a quadrature signal generated by digital quadrature modulation or a quadrature difference due to the digital quadrature modulation. Since the position error of the signal point arrangement which occurs is compensated, in addition to the effect of claim 1, the operation which compensates for the error of the signal point position caused by the operation error of the circuit of the actual digital quadrature modulator is operated. There is an effect that a method for obtaining a highly accurate digital quadrature modulation signal can be provided.

According to the third aspect of the present invention, in particular, since the error of the circuit operation inherent in the digital quadrature modulator is compensated, the operation of the digital quadrature modulator is added to the effect of the first aspect. There is an effect that it is possible to provide a method of obtaining a stable and accurate digital quadrature modulation signal that operates by compensating for the error of the signal point position caused by the processing operation.

According to the fourth aspect of the present invention, position error compensation is performed especially for two subcarriers arranged in the positive and negative directions by the same frequency with respect to the center carrier frequency. Therefore, in addition to the effect of claim 1, a stable and highly accurate digital quadrature modulation signal that operates by compensating for an error in a signal point position caused by interference between two subcarriers arranged at the same frequency in the positive and negative directions. This has the effect of providing a method for obtaining

According to the fifth aspect of the present invention, the baseband signals of the real part and the imaginary part obtained by digital orthogonal modulation, for example, by IFFT, are digital orthogonal frequency division of an intermediate frequency band as digital signals. Even when the digital quadrature modulator generates a digital quadrature modulation signal by alternately calculating a real part signal and an imaginary part signal from the IFFT arithmetic unit when converting the signal into a multiplex modulated signal, An error signal generated due to a difference between the operation timings of the partial signal and the imaginary part signal is converted into a real part,
And a signal point arrangement for canceling an operation error when a signal of an imaginary part is generated, so that IFFT operation is performed. Therefore, a digital quadrature modulation that does not include an error signal and is stable and highly accurate by digital quadrature modulation signal generation processing. There is an effect that a transmission signal generation device that generates a signal can be configured.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an orthogonal frequency division multiplex modulation apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an analog quadrature modulator.

FIG. 3 is a diagram illustrating a configuration of a quadrature modulator including a digital circuit.

FIG. 4 is a chart showing the operation timing of the digital quadrature modulator in a chart.

FIG. 5 is a chart showing an operation timing of a digital quadrature modulator having a short sample period in a chart.

FIG. 6 shows a state of a subcarrier having a phase angle α and rotating at an angular velocity + ω _n and having an amplitude A on a two-dimensional plane with imaginary and real axes.

FIG. 7 shows equations (6) to (9) showing signal vectors.

FIG. 8 shows vectors of terms 61 and 63 of the equation (6) on a two-dimensional plane with imaginary and real axes.

FIG. 9 shows a vector of terms 62 and 64 of equation (6) on a two-dimensional plane with imaginary and real axes.

FIG. 10 shows the vector of terms 72 and 74 in equation (7) as an imaginary number,
It is shown on a two-dimensional plane with real axes.

11 is a diagram showing a vector of terms 71 and 73 of equation (7) as an imaginary number,
It is shown on a two-dimensional plane with real axes.

FIG. 12 is a diagram showing mapping points for obtaining a signal output of an angular frequency ωt compensated by a digital quadrature modulator.

FIG. 13 is a diagram showing mapping points for obtaining a signal output of angular frequency −ωt compensated by a digital quadrature modulator.

FIG. 14 is a table for obtaining compensated mapping points when each of the positive and negative sub-carriers of the same frequency is modulated by QPSK, and each carrier is assigned four signal points.

[Explanation of symbols]

 Reference Signs List 11 data mapping circuit 12 mapping table 13 IFFT operation circuit 15 digital quadrature modulation circuit 16 intermediate frequency oscillator 17 DA converter

Claims (5)

[Claims] 1. A two-dimensional plane centered on a real part signal and an imaginary part signal is divided into a plurality of regions, and a central position for designating each of the divided regions is defined as a signal point. As well as, according to the content of the digital information signal to be transmitted, sequentially allocated to a specific signal point of the plurality of signal points, a real part signal and an imaginary part signal at each of the sequentially allocated signal points. A method for generating a transmission signal that converts a signal point information into a high-frequency signal by performing digital modulation and digital quadrature modulation on the signal point information, wherein digital modulation is performed on the signal point information assigned to the position of the signal point. A first step of determining a modulation signal point obtained by performing digital quadrature modulation as a compensation signal point at a position that is a point target with respect to the signal point position; A second step of allocating a digital information signal to be assigned to the compensation signal point determined in the first step; and digitally and digital quadrature modulation of signal point information at the compensation signal point allocated in the second step. At least a third step of generating a high-frequency signal. 2. The position of the compensation signal point in the first step includes a phase difference and an amplitude difference between an in-phase signal and a quadrature signal generated by the digital modulation and the digital quadrature modulation.
2. The transmission signal generation method according to claim 1, wherein the position of the signal point compensates for an error caused by the orthogonality difference of the digital quadrature modulator. 3. The position of the compensation signal point in the first step is a position of a signal point in which an error caused by a timing difference between an in-phase signal and a quadrature signal processed by the digital quadrature modulation is compensated. The transmission signal generation method according to claim 1, wherein: 4. A two-dimensional plane centered on a real part signal and an imaginary part signal is divided into a plurality of regions, and a central position for designating each of the divided regions is defined by a signal point. And sequentially assigns a first-system digital information signal to be transmitted to a specific signal point among the plurality of signal points according to the content thereof, and a real part signal and an imaginary number at each of the sequentially assigned signal points. A first signal point information comprising a partial signal is generated as a first modulation signal by a first carrier frequency, and a second system of digital information signals to be transmitted is transmitted in accordance with the content thereof. A second signal consisting of a real part signal and an imaginary part signal at each of the sequentially assigned signal points.
Using digital modulation means for generating signal point information as a second modulation signal using a second carrier frequency having the same frequency as the first carrier frequency but having a different polarity, wherein the second signal generated by the digital modulation means is used. In a transmission signal generation method for generating a transmission signal obtained by digitally orthogonally modulating a first and second modulation signal and converting the signal into a high-frequency signal, the signals related to the first and second digital information signals to be transmitted The first and second modulation signal points obtained by performing digital modulation and digital quadrature modulation on the signal point information allocated to the position of the point are used as the target positions for the respective signal points. A first step for determining first and second compensation signal points, and the first and second digital information signals to be transmitted, the first and second compensation signal points being determined in the first step. And a second step of allocating to the second compensation signal points, and digital signal and digital quadrature modulation of each of the signal point information at the first and second compensation signal points allocated in the second step, the high-frequency signal And a third step of generating a transmission signal. 5. A two-dimensional plane centered on a real part signal and an imaginary part signal is divided into a plurality of regions, and a central position for designating each of the divided regions is a signal point. As well as, according to the content of the digital information signal to be transmitted, sequentially allocated to a specific signal point of the plurality of signal points, a real part signal and an imaginary part signal at each of the sequentially allocated signal points. In a transmission signal generating apparatus for generating a transmission signal converted into a high-frequency signal by performing digital modulation and digital quadrature modulation on the signal point information, the digital modulation is performed on the signal point information assigned to the position of the signal point. And a compensation signal point setting means for determining a modulation signal point obtained by performing digital quadrature modulation as a compensation signal point at a position to be pointed with respect to the position of the signal point; Mapping means for allocating a digital information signal to be transmitted to the compensation signal point set by the compensation signal point setting means; digital modulation and digital quadrature modulation of the signal point information at the compensation signal point allocated by the mapping means And a high-frequency signal generating means for generating a high-frequency signal.